Urea is found in the aqueous effluents of a number of commercial plants. These streams have been traditionally discharged to the environment because commercial removal technology has not been available for treatment of these streams.
The only method of treating urea-containing aqueous streams has been steam treatment wherein the urea is hydrolyzed at high temperatures under high pressure. This treatment, as can be imagined, would be very expensive when applied to large-volume, low-concentration streams.
U.S. Pat. No. 2,744,840 to Daniels, et al. discloses a method of sugar purification ion exchange by removing Na.sup.+, K.sup.+, Ca.sup.++, Mg.sup.++ and the like with a hydrogen cation exchange bed in series with an anion exchange bed.
U.S. Pat. No. 3,655,395 discloses a process for treating odiferous industrial and municipal waste materials by adding formaldehyde, nitric acid and urea to the waste materials in sequence. The urea reacts with the residual formaldehyde in the mixture, in the presence of the nitric acid as a catalyst, in order to form a urea-formaldehyde condensation product.
U.S. Pat. No. 3,313,726 to Campbell discloses a process for regenerating strongly acidic cation exchange resins and strongly basic anion exchange resins to substantially their original ion-exchange capacity when the regeneration is preceded by a defouling step.
Rohm and Haas, "Amber-Hi-Lites," (October 1971) contains a chart of the chemical and physical properties and a summary of applications of the Amberlite and Amberlyst ion exchange resins.
U.S. Pat. No. 3,316,717 to Mastrorillo discloses a process of regenerating cation exchange resins and, particularly, a process for regenerating, in a hydrogen cycle, cation resins used in water treatment plants. An at least partially spent cationic exchange resin containing cations removed from water is treated with a solution containing a monobasic acid selected from the group consisting of hydrochloric acid, hydrobromic acid, nitric acid, nitrous acid, acetic acid and propionic acid so as to form a solution containing the salt of a monobasic acid and the cations.
U.S. Pat. No. 3,775,088 to Higgins discloses a process for treating fertilizer plant waste streams containing ammonium, hardness metal and nitrate values to recover an ammonium nitrate fertilizer and a demineralized and substantially nitrate-free aqueous stream. This process includes initially removing the ammonium ion and hardness metal ion values from the fertilizer plant waste stream with a cation exchange resin bed and then contacting the essentially ammonium and hardness ion-free aqueous stream with an anion exchange resin bed to recover a second ammonium nitrate fertilizer stream and a demineralized and nitrate-free aqueous stream.
This patent states at Column 7, lines 35-40 that "prior to introducing the fertilizer plant waste aqueous stream into the cation exchange column loop 10, preferably this stream is passed through one or more filters to remove particulate matter and urea." The fertilizer plant waste aqueous stream which is passed through one or more filters to remove particulate matter and urea is a non-acid environment. The nitrous acid of the present invention may not be substituted for the filtration step in Higgins because nitrous acid will not remove urea in said non-acid, mineral ion containing solution, i.e. nitrous acid will not react with urea in a non-acid environment. Moreover, the nitrous acid of the present invention and the nitric acid employed as a regenerating agent in Higgins may not be successfully interchanged because nitrous acid is not as strong as nitric acid and is considered an unstable compound and therefore, nitrous acid would not be suitable as a regenerating agent.
Astle and Shelton, Organic Chemistry, 2nd Edition (New York, 1959), p. 208, shows the laboratory reaction of urea with nitrous acid. The reaction or urea and nitrous acid in Astle is a quantitative analysis laboratory experiment. This reaction does not go to the "heart" of the present invention, which is the immediate destruction of urea in conjunction with ion exchange removal of pollutants from waste water. The Astle publication does not fairly suggest the use of nitrous acid in the destruction of urea in commercial waste streams which contain other pollutants.
U.S. Pat. No. 3,113,837 to Scanley discloses a process for obtaining a stabilized nitrous acid. Particularly, this patent relates to a process for preparing a stabilized, concentrated solution of nitrous acid free from contaminants. Scanley states at Column 1, lines 23 to 31 as follows:
" . . . , it is also known that nitrous acid is a useful reactant in many varied organic reactions. Since such reactions are often conducted in a minimal aqueous environment, the preparation of a dilute aqueous solution of nitrous acid contaminated with mineral acids and salts cannot be readily utilized as an article of commerce."